strange dropping of idle speed.

[bigrobby]

99.5 A4 1.8t apr 93 octane 143k

first of all, on occasion it starts up a little strange. instead of jumpin right up to ~1200rpm when i crank it, it stumbles at around 500 for a half a second before running normal.

then on a long trip last night i stopped for gas, let it idle for about 5 minutes before i turned it off, which is what i normally do.

it started rough and then about every 7 seconds or so the idle would drop down to about 500 then jump back up. it did this for a minute or two. AC was off. no check engine or anything abnormal. Afterwards it ran just fine but I still have good reason to be concerned, my car never acts strange like that.

any ideas?

also, on some turbo diesel boats i work on, the actual turbine can get stuck, and we actually spin it free by hand. anyone ever heard of that happening on an audi?.....cause that would explain the rough initial start if the turbine was stuck for a moment. I've never actually heard of that on a car.

thanks

[hepgot]

i've recently been having similar problems. Car would idle terrible. Felt like the ECU was running through different RPM's looking for a good idle spot and upon driving car would go into limp mode. Unplugged the MAF and fixed the whole going into limp mode thing, so I got a new MAF and its running good. However, idle is still not right, I'm thinking it could be a bad O2 sensor, or do these cars have a throttle position sensor or idle control valve?

[bigrobby]

my problem is at idle only. never had any other running problem. i think if there was a problem with the 02 sensor, of course the pre-cat one, it would CEL would come on. besides, at least in my case, 02 sensor shouldnt be used right when it starts, it has to heat up first, I'm sure there is a tps but the MAF will really determine how much fuel to add to however much air is coming through. IF my MAF was bad or dirty i dont think it would run right at all other speeds

[keeganhartman]

What about tb?